Question on turbulent air penetration speed

[rchwallace]

Hey guys......

I thought I would give you a bit on VNAV. The Level D sim is very realisitic so the VNAV behaviour is well moddeled.... anyhoo. I will keep
it simple but maybe add some stuff that may help you.

If you are in path (VNAV PTH) in the decent the aircraft will maintain the decent "path".... it will keep the aircraft decending at a
programmed path from one constraint to the next. For the 250 and 10000ft area this can be a problem if the winds or path are not
working quite right for the aircraft........ what I mean by this is that when in PATH the aircraft will not protect your speed...... its priority is the
path. It has programed its decent point etc etc lets say for an idle decent but with the different variables it will have to vary your speed
from the programmed speed to maintain the path. Sometimes the winds can be quite strong and will vary your path extensively and as a
result the aircraft will not be able to maintain the speed. This happens quite often and the aircraft may start going slow or fast dependind on what the winds are doing..... To fix this you either need thrust if slow or speedbrakes if fast...... OR

You can open the speed window on the MCP and put the decent mode into VNAV SPD this then changes the priority of VNAV to decend to
your cleared altitudes at the speed in the window..... it will hold the speed and varry the decent path to reach the desired decent altitude.
This can result in a longer decent and if ATC are vectoring you in close you could end up slightly out... but I use this in the A/C when
cleared an ATC speed. VNAV is programmed but I keep the window open as it will decend on speed rather than path. FLCH will do the
same in that it will keep a good speed for you..... initially it will go into IDLE but after will go into HOLD. (For the autothrottle) I use the
precision thrust levers (PFC) and with level D I am able to adjust the thrust setting when the AT mode is in HOLD as in real aircraft.

Dont know if this helps at all with the problems stated but.........

Regards



Post Edited ( 08-02-05 04:56 )